Slack, a business communication app created by Flickr cofounder Stewart Butterfield, is growing like crazy. In just six months, it’s added more than 125,000 active users, and each of them is using the app for almost 10 hours a day, according to Slack.

On Wednesday, billionaire investor Marc Andreessen, who also happens to be a Slack investor, tweeted a little chart that perfectly shows the kind of growth Slack has been enjoying.